The invention relates to an improvement of ceramic filters that are used to separate and capture solids from a gas or a liquid.
As is well known, an alumina-based asymmetric ceramic membrane is used as a ceramic porous separating membrane that is employed as an in-line gas filter, etc. in semiconductor manufacturing processes. Since this membrane was originally developed for gas separation in treating a uranium material, the initial models were configured to have a simple shape, i.e., a single tube shape, to insure reliability as required in large plants. This single tube shape can most suitably be formed by extrusion molding, and later developed lotus-rhizome-shaped tubes are produced by the same molding technique.
In either of the single tube or lotus-rhizome-shaped tube, the separating membrane is formed on the inner surface of the tube or holes. The membrane has the same chemical composition as the support member, and is formed by sintering a powder of small particles.
However, in each of the single tube and the lotus-rhizome-shaped tube, the overall shape is determined by the support member which is responsible for the tube strength, and the separating membrane is formed on the inner surface of the single tube or the inner surfaces of the individual holes of the lotus-rhizome-shaped tube. Therefore, it is difficult to increase the membrane area relative to the overall volume of the tubular ceramic membrane structure. To insure a sufficient membrane area, the ceramic membrane structure becomes large and, as a result, a membrane module becomes bulky, eventually necessitating an unduly large separating machine.
As a further problem, the recent membrane technology is such that even the design concept of the ceramic module is determined by the tubular ceramic membrane structure. More specifically, modules of a little less than 1 m in length are made fundamental ones, and smaller membrane modules are produced by cutting the ceramic membrane structures and fitting the cut parts with necessary parts such as a casing and gaskets. Therefore, the minimum diameter of the modules is restricted by the thickness of the tubular ceramic membrane structure.